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| United States Patent |
5,028,503
|
|
Chang
|
July 2, 1991
|
Photohardenable electrostatic element with improved backtransfer
characteristics
Abstract
Photohardenable electrostatic master with improved backtransfer
characteristics comprising
(1) an electrically conductive substrate, and
(2) a layer of photohardenable composition consisting essentially of
(a) at least one organic polymeric binder,
(b) at least one compound having at least one ethylenically unsaturated
group, and
(c) a photoinitiator or photoinitiator system, and
(d) an acidic additive as defined.
A xeroprinting process is described using the master. The master is used in
graphic arts, color proofing which duplicates images produced by printing,
preparation of printed circuit boards, resists, soldermasks, etc.
| Inventors:
|
Chang; Catherine T. (Wilmington, DE)
|
| Assignee:
|
E. I. Du Pont de Nemours and Company (Wilmington, DE)
|
| Appl. No.:
|
410655 |
| Filed:
|
September 21, 1989 |
| Current U.S. Class: |
430/281.1; 430/56; 430/283.1 |
| Intern'l Class: |
G03C 001/725; G03C 001/73; G03G 015/00 |
| Field of Search: |
430/281
|
References Cited
U.S. Patent Documents
| 4210711 | Jan., 1980 | Kitajima et al. | 430/325.
|
| 4264710 | Apr., 1981 | Kondoh et al. | 430/281.
|
| 4347303 | Aug., 1982 | Asano et al. | 430/272.
|
| 4351893 | Sep., 1982 | Anderson | 430/281.
|
| 4725518 | Feb., 1988 | Carmichael et al. | 430/132.
|
| 4732831 | Mar., 1988 | Risenfeld et al. | 430/49.
|
| 4732881 | Mar., 1988 | Riesenfeld et al. | 430/49.
|
| 4814246 | Mar., 1989 | Lehmann et al. | 430/66.
|
| 4818660 | Apr., 1989 | Blanchet-Fincher et al. | 430/281.
|
| 4839314 | Jul., 1989 | Blanchet-Fincher et al. | 430/49.
|
Primary Examiner: McCamish; Marion E.
Assistant Examiner: Crossan; S.
Claims
What is claimed is:
1. A high resolution, photohardenable electrostatic master comprising:
(1) an electrically conductive substrate bearing
(2) a layer of photohardenable composition consisting essentially of
(a) at least one organic polymeric binder,
(b) at least one compound having at least one ethylenically unsaturated
group,
(c) a photoinitiator or photoinitiator system that activates polymerization
of the ethylenically unsaturated compound upon exposure to actinic
radiation, and
(d) an acidic additive selected from the group consisting essentially of:
(1) compounds of the general formula:
R--NH--R'
where R is R.sup.1 --SO.sub.2,
##STR16##
R' is H, acyl, alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl,
##STR17##
halogen or heterocyclic groups; R and R' when taken together may form a
heterocyclic ring; R.sup.1, R.sup.2 and R.sup.3 may be the same or
different and are alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, acyl, halogen or heterocyclic
groups;
(2) phosphonic acids of the general formula:
##STR18##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, halogen or heterocyclic
groups; and
(3) polybasic carboxylic acids having at least two acid groups.
2. A photohardenable electrostatic master according to claim 1 wherein the
acid additive (1) is of the formula: R.sup.1 --SO.sub.2 --NH--R' where
R.sup.1 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon atoms,
substituted alkyl and substituted aryl; R' is H, acyl, alkyl of 1 to 12
carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl or
substituted aryl.
3. A photohardenable electrostatic master according to claim 2 wherein the
acidic additive represented by the formula is a sulfonamide.
4. A photohardenable electrostatic master according to claim 3 wherein the
acidic additive is a mixture of o- and p-toluenesulfonamide.
5. A photohardenable electrostatic master according to claim 3 wherein the
acidic additive is alpha-toluenesulfonamide.
6. A photohardenable electrostatic master according to claim 3 wherein the
acidic additive is p-(p-toluenesulfonamido) diphenylamine.
7. A photohardenable electrostatic master according to claim 2 wherein the
acidic additive represented by the formula is a sulfonimide.
8. A photohardenable electrostatic master according to claim 7 wherein the
acidic additive is benzoic sulfonimide.
9. A photohardenable electrostatic master according to claim 1 wherein the
acidic additive is a sulfonylurea.
10. A photohardenable electrostatic master according to claim 1 wherein the
acidic additive (1) is of the formula:
##STR19##
wherein R.sup.1 and R' may be the same or different and are alkyl of 1 to
12 carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl,
substituted aryl, heterocyclic 5- or 6-membered rings, and R.sup.1 and R'
when taken together may form heterocyclic 5- or 6-membered rings or
condensed rings.
11. A photohardenable electrostatic master according to claim 10 wherein
the acidic additive is a phthalimide.
12. A photohardenable electrostatic master according to claim 10 wherein
the acidic additive is a diacetamide.
13. A photohardenable electrostatic master according to claim 10 wherein
the acid additive of the formula is a heterocyclic 5- or 6-membered ring
or condensed ring.
14. A photohardenable electrostatic master according to claim 13 wherein
the acidic additive is parabanic acid.
15. A photohardenable electrostatic master according to claim 1 wherein the
acidic additive (1) is of the formula:
##STR20##
wherein R.sup.1, R', R.sup.2 may be the same or different and are alkyl of
1 to 12 carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl,
substituted aryl, halogen, or heterocyclic 5- or 6-membered rings.
16. A photohardenable electrostatic master according to claim 15 wherein
the acidic additive is phenyl N-phenylphosphonamido chloridate.
17. A photohardenable electrostatic master according to claim 1 wherein the
acidic additive (2) is of the formula:
##STR21##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, halogen or heterocyclic
groups.
18. A photohardenable electrostatic master according to r claim 17 wherein
the acidic additive is benzene phosphonic acid.
19. A photohardenable electrostatic master according to claim 1 wherein the
acidic additive (3) is of the formula HO.sub.2 C--R.sup.5 --CO.sub.2 H
wherein R.sup.5 is aliphatic of 0 to 12 carbon atoms which can be
saturated or unsaturated, substituted or unsubstituted; aryl of 6 to 30
carbon atoms, substituted alkyl or substituted aryl.
20. A photohardenable electrostatic master according to claim 19 wherein
the acidic additive is phthalic acid.
21. A photohardenable electrostatic master according to claim 19 wherein
the acidic additive is maleic acid.
22. A photohardenable electrostatic master according to claim 19 wherein
the acidic additive is diphenic acid.
23. A photohardenable electrostatic master according to claim 1 wherein a
chain transfer agent is present.
24. A photohardenable electrostatic master according to claim 23 wherein a
chain transfer agent is 2-mercaptobenzoxazole.
25. A photohardenable electrostatic master according to claim 23 wherein
the binder (a) is polymethyl methacrylate, ethylenically unsaturated
compound (b) is ethoxylated trimethylol propane triacrylate,
photoinitiator or photoinitiating system (c) is
2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)biimidazol
e, acidic additive (d) is a mixture of o-and p-toluene sulfonamide, and the
chain transfer agent is 2-mercaptobenzoxazole.
26. A photohardenable electrostatic master according to claim 23 wherein
the binder (a) is polymethyl methacrylate, ethylenically unsaturated
compound (b) is ethoxylated trimethylol propane triacrylate,
photoinitiator or photoinitiating system (c) is
2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)biimidazol
e, acidic additive (d) is benzoic sulfonimide, and the chain transfer agent
is 2-mercaptobenzothiazole.
27. A photohardenable electrostatic master according to claim 1 wherein the
binder (a) is selected from the group consisting of acrylate and
methacrylate polymers and copolymers, vinyl polymers and copolymers,
polyvinyl acetals, polycarbonates, polysulfones, polyetherimides,
polyphenylene oxides, polyesters, polyurethanes, butadiene copolymers,
cellulose esters and cellulose ethers.
28. A photohardenable electrostatic master according to claim 1 wherein the
polymeric binder (a) is a mixture of a polymeric binder having a Tg
greater than 80.degree. C. and a polymeric binder with a Tg less than
70.degree. C.
29. A photohardenable electrostatic master according to claim 28 wherein
the binder having a Tg greater than 80.degree. C. is selected from the
group consisting of acrylate and methacrylate polymers and copolymers,
vinyl polymers and copolymers, polyvinyl acetals, polycarbonates,
polysulfones, polyetherimides, and polyphenylene oxides.
30. A photohardenable electrostatic master according to claim 29 wherein
the binder is poly(styrene/methyl methacrylate).
31. A photohardenable electrostatic master according to claim 28 wherein
the binder with a Tg less than 70.degree. C. is selected from the group
consisting of acrylate and methacrylate polymers and copolymers, vinyl
polymers and copolymers, polyvinyl acetals, polyesters, polyurethanes,
butadiene copolymers, cellulose esters and cellulose ethers.
32. A photohardenable electrostatic master according to claim 31 wherein
the binder is poly(ethyl methacrylate).
33. A photohardenable electrostatic master according to claim 1 wherein a
monomeric compound (b) having ethylenic unsaturation is an acrylate or
methacrylate compound having at least two terminal ethylenically
unsaturated groups.
34. A photohardenable electrostatic master according to claim 33 wherein
compound (b) is glycerol propoxylated triacrylate.
35. A photohardenable electrostatic master according to claim 1 wherein the
at least one compound (b) is a mixture of glycerol propoxylated
triacrylate and trimethylolpropane triacrylate.
36. A photohardenable electrostatic master according to claim 1 wherein the
photoinitiator (c) is a 2,4,5triphenylimidazolyl dimer.
37. A photohardenable electrostatic master according to claim 36 wherein
the photoinitiator is
2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)biimidazol
e.
38. A photohardenable electrostatic master according to claim 36 wherein
the photoinitiator is
2,2'-bis(o-chlorophenyl)-4,4',5,5'-bis(m-methoxyphenyl)-biimidazole.
39. A photohardenable electrostatic master according to claim 36 wherein a
chain transfer agent is present.
40. A photohardenable electrostatic master according to claim 39 wherein
the chain transfer agent is 2-mercaptobenzoxazole.
41. A photohardenable electrostatic master according to claim 39 wherein
the chain transfer agent is 2-mercaptobenzothiazole.
42. A photohardenable electrostatic master according to claim 1 wherein the
photoinitiator (c) is a substituted or unsubstituted polynuclear quinone.
43. A photohardenable electrostatic master according to claim 42 wherein
the photoinitiator is 2-ethylanthraquinone.
44. A photohardenable electrostatic master according to claim 1 wherein the
photoinitiator (c) is a benzoin ether.
45. A photohardenable electrostatic master according to claim 44 wherein
the photoinitiator is benzoin methyl ether.
46. A photohardenable electrostatic master according to claim 1 wherein a
sensitizer compound is present.
47. A photohardenable electrostatic master according to claim 46 wherein
the sensitizer compound is
2-{9'-(2',3',6',7'-tetrahydro-lH,5H-benzo[i,j]-quinolyidene))-5,6-dimethox
y-1-indanone.
48. A photohardenable electrostatic master according to claim 1 wherein the
layer of photohardenable composition in combination with component (d)
contains
(a) a binder selected from the group of poly(styrene/methylmethacrylate)
and poly(methyl methacrylate),
(b) a monomeric compound selected from the group consisting of glycerol
propoxylated triacrylate, trimethylol propane triacrylate and mixtures
thereof, and
(c)
2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)biimidazol
e, and 2-mercaptobenzoxazole as a chain transfer agent.
49. A photohardenable electrostatic master according to claim 1 wherein the
layer of photohardenable composition has present the following components:
polymeric binder (a), 40 to 70% by weight, compound (b), 15 to 40% by
weight, the photoinitiator (c), 1 to 20% by weight, and acidic additive
(d), 1 to 10% by weight, the weight percentages being based on the total
weight of the photohardenable composition.
Description
FIELD OF THE INVENTION
This invention relates to a photohardenable electrostatic master for
xeroprinting. More particularly this invention relates to a
photohardenable electrostatic master having on an electrically conductive
substrate a layer of a photohardenable composition which contains an
organic polymeric binder, compound having at least one ethylenically
unsaturated group, photoinitiator or photoinitiator system, and an acidic
additive.
BACKGROUND OF THE INVENTION
Photopolymerizable compositions and films containing binder, monomer,
initiator and chain transfer agent are described in the prior art and sold
commercially. One important application of photopolymerizable layers is in
graphic arts. A need exists in the graphic arts field to render faithful
proofs which describe the image quality that can be attained prior to the
printing process. Specifically, it is desirable to demonstrate the
appearance and the quality of the printed product prior to its production.
The actual mounting of printing plates on a printing press is expensive
and time consuming. Adjustments in the printing plate are sometimes
necessary in order to achieve the right tonal range, etc. In other cases,
it is necessary to remake the plate, if there are any defects in it, such
as may be caused by improper exposure of a color separation negative from
which a plate is generated.
A number of proofing processes are commercially available. Several of these
are capable of giving separate films containing colored images, which on
superimposition give a multicolored image that approximates the ultimate
pattern generated on the printing press. Other processes depend on
selectively toning layers of partially exposed surfaces, to give surprints
which more closely resemble the images that are generated on printing than
the overlay films described earlier. These processes, however, do not
result in the most desirable proof, i.e., one which gives a surprint that
is indeed a printed image on unmodified paper stock as is used in
printing. Furthermore, the previously cited methods do not permit the
facile formation of multiple prints as are frequently required in the
printing industry, as for example, when the proof is employed as a press
guide in two different locations. The technology described herein
addresses the need to make multiple surprints and to overcome the
limitations of several commercial proofing processes.
Photopolymerizable layers are currently being used as electrostatic masters
for analog color proofing. For this application, a photopolymerizable or
photohardenable layer is coated on an electrically conductive substrate
and contact exposed with an ultraviolet (UV) source through a half-tone
color separation negative. The photopolymerizable composition hardens in
the areas exposed with an ultraviolet source due to polymerization and
remains in a softer state elsewhere. The differences between the exposed
and unexposed areas are apparent in the transport properties, i.e., the
unexposed nonpolymerized areas conduct electrostatic charge while the UV
exposed areas are substantially non-conductive. By subjecting the exposed
photopolymerizable layer to a corona discharge a latent electrostatic
image is obtained consisting of electrostatic charge remaining only in
nonconducting or exposed areas of the photopolymerizable layer. This
charged latent image can be developed by application of a liquid or dry
electrostatic developer thereto. When the developer has a charge opposite
to that of the corona charge, the developer selectively adheres to the
exposed or polymerized areas of the photopolymerizable layer. It is
desirable to permit selective toner deposition on the imagewise exposed
and charged photopolymerizable layer within a short time after charging.
That is, there is the need for a more rapid decay of the unexposed
(background) areas of the photopolymerizable or photohardenable layer. As
long as a significant amount of charge resides on the unexposed
(background) areas, developer will be deposited on these areas, therefore
requiring a longer time period between charging and applying developer if
background coloring is to be avoided. Although single color
electrophotography is a reliable mature technique, color on color
electrophotography is relatively new and the application of four different
color developer layers on top of each other has its own problems.
While slow charge decay is a problem, we consider the most serious problem
in the preparation of color proofs using electrostatic systems to be
backtransfer. It was discovered that when a second color developer was
transferred from the photohardenable master on top of an existing image on
paper, the developer layer originally on the paper partially
backtransferred to the electrostatic master during the second transfer.
The backtransfer problem worsens when dealing with four layers of
developers, since in that case all the previously transferred colors can
partially backtransfer from the paper onto the surface of the master.
Therefore, the final image on paper is unacceptable due to its degraded
color and resolution. In attempting to deal with the backtransfer problem
we noted, for example, that the negatively charged toner particles in the
liquid electrostatic developer when backtransferred surprisingly were
found to be neutral or have positive charges. This charge reversal or
neutralization suggested that the large transfer fields partially
electrolyzed the toner particles. Charge reversal also implied that toner
particles will backtransfer since an electric field that drives negative
particles towards the paper would drive positive particles towards the
master.
Furthermore, we learned that the toner neutralization occurred on the paper
and at the photopolymer electrodes. Backtransfer could be overcome by
blocking the toner neutralization either by using dielectric coated paper
or by washing the photopolymerizable layer surface with a solution of
charge director and carrier liquid with conductivities above a determined
threshold value. These approaches, however, are not practical as it is
undesirable to use non-standard papers and to wash the surface of the
photopolymerizable layer.
Backtransfer has not been observed when the charged surface is a selenium
photoconductor and is not a serious problem on silver halide masters.
Charged photopolymerizable layers are different with respect to
backtransfer. For example, up to 80% of a toned image can be
backtransferred to a photopolymerizable master under high ambient
humidities and high transfer field conditions. It is therefore believed
that the resistivity of the transfer zone and the nature of the charge
carrier play important roles in developer backtransfer. In an attempt to
overcome the disadvantage of backtransfer, the photopolymerizable
composition was formulated to include additives that modified the
electrochemistry at the surface of the photopolymerizable layer so that
the particular liquid electrostatic developer would transfer from the
master onto the paper or subsequent transferred image layer without
electrically modifying the toner particles in the developer.
It has now been found that charge decay of the unexposed areas of a
photopolymerizable or photohardenable layer and backtransfer of previously
developed and transferred images to the surface of the photohardenable
layer of an electrostatic master can be greatly improved by introducing
into the photohardenable composition used to form the layer an acidic
additive of the type described below.
SUMMARY OF THE INVENTION
In accordance with this invention there is provided a high resolution,
photohardenable electrostatic master comprising:
(1) an electrically conductive substrate bearing
(2) a layer of photohardenable composition consisting essentially of
(a) at least one organic polymeric binder,
(b) at least one compound having at least one ethylenically unsaturated
group,
(c) a photoinitiator or photoinitiator system that activates polymerization
of the ethylenically unsaturated compound upon exposure to actinic
radiation, and
(d) an acidic additive selected from the group consisting essentially of:
(1) compounds of the general formula:
R--NH--R'
where R is R.sup.1 --SO.sub.2,
##STR1##
R' is H, acyl, alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl,
##STR2##
halogen or heterocyclic groups; R and R' when taken together may form a
heterocyclic ring; R.sup.1, R.sup.2 and R.sup.3 may be the same or
different and are alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, acyl, halogen or heterocyclic
groups;
(2) phosphonic acids of the general formula:
##STR3##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, halogen or heterocyclic
groups; and
(3) polybasic carboxylic acids having at least two acid groups.
In accordance with an embodiment of this invention there is provided a
xeroprinting process comprising
(A) exposing imagewise to actinic radiation a photohardenable electrostatic
master comprising
(1) an electrically conductive substrate bearing
(2) a layer of photohardenable composition consisting essentially of
(a) at least one organic polymeric binder,
(b) at least one compound having at least one ethylenically unsaturated
group, and
(c) a photoinitiator or photoinitiator system that activates polymerization
of the ethylenically unsaturated compound upon exposure to actinic
radiation, and
(d) an acidic additive selected from the group consisting essentially of:
(1) compounds of the general formula:
R--NH--R'
where R is R.sup.1 --SO.sub.2,
##STR4##
R' is H, acyl, alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl,
##STR5##
halogen or heterocyclic groups; R and R' when taken together may form a
heterocyclic ring; R.sup.1, R.sup.2 and R.sup.3 may be the same or
different and are alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, acyl, halogen or heterocyclic
groups;
(2) phosphonic acids of the general formula:
##STR6##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, halogen or heterocyclic
groups; and
(3) polybasic carboxylic acids having at least two acid groups.
(B) charging the photohardenable master electrostatically,
(C) applying an oppositely charged electrostatic toner, and
(D) transferring the toned image to a receptor surface.
DETAILED DESCRIPTION OF THE INVENTION
Throughout the specification the below-listed terms have the following
meanings:
In the claims appended hereto "consisting essentially of" means the
composition of the photohardenable layer does not exclude unspecified
components which do not prevent the advantages of the layer from being
realized. For example, in addition to the primary components, there can be
present additional components, such as sensitizers, including visible
sensitizers, hydrogen donors or chain transfer agents (preferred), both of
which are considered part of the photoinitiator system; thermal
stabilizers or thermal polymerization inhibitors, photoinhibitors,
antihalation agents, UV absorbers, release agents, colorants, surfactants,
plasticizers, electron donors, electron acceptors, etc.
Photohardenable and photopolymerizable are used interchangeably in this
invention.
Monomer means simple monomers, as well as polymers, usually of molecular
weights below 1500, having at least one, preferably two or more, ethylenic
groups capable of crosslinking or addition polymerization.
The photohardenable (photopolymerizable) layer of the electrostatic master
consists essentially of at least one organic polymeric binder, a compound
having at least one ethylenically unsaturated group which can be a
monomer, a photoinitiator or photoinitiator system, and an acidic additive
as more fully described below. Preferably a chain transfer agent is also
present. In addition to the primary ingredients, other ingredients which
do not prevent the advantages of the invention from being achieved. These
other ingredients which can also be present are set out below. Useful
polymeric binders, ethylenically unsaturated compounds, photoinitiators,
including preferred hexaarylbiimidazole compounds (HABI's) and chain
transfer agents are disclosed in Chambers U.S. Pat. No. 3,479,185, Baum et
al. U.S. Pat. No. 3,652,275, Cescon U.S. Pat. No. 3,784,557, Dueber U.S.
Pat. No. 4,162,162, and Dessauer U.S. Pat. No. 4,252,887, the disclosures
of each of which are incorporated herein by reference.
The primary components include:
BINDERS
Suitable binders include: acrylate and methacrylate polymers and co- or
terpolymers; vinyl polymers and copolymers, polyvinyl acetals, such as
polyvinyl butyral and polyvinyl formal; vinylidene chloride copolymers
(e.g., vinylidene chloride/acrylonitrile, vinylidene chloride/methacrylate
and vinylidene chloride/vinyl acetate copolymers), polyesters,
polycarbonates, polyurethanes, polysulfones, polyetherimides and
polyphenylene oxides, synthetic rubbers such as butadiene copolymers,
e.g., butadiene/acrylonitrile copolymers and
chloro-2-butadiene-1,3-polymers; cellulose esters, e.g., cellulose
acetate, cellulose acetate succinate and cellulose acetate butyrate;
cellulose ethers, polyvinyl esters, e.g., polyvinyl acetate/acrylate,
polyvinyl acetate/methacrylate and polyvinyl acetate; polyvinyl chloride
and copolymers, e.g., polyvinyl chloride/acetate; polystyrene, etc.
Preferred binders are poly(styrene/methyl methacrylate) and polymethyl
methacrylate. Blends of high and low Tg binders have been found to improve
environmental latitude of the photopolymerizable layers. In general, it
has been found that a high Tg binder (approximately in the range of
80.degree.-110.degree. C.) and a low Tg binder (approximately in the range
of 50.degree.-70.degree. C.) are preferred. Types of high Tg resins useful
as a binder include: certain acrylate and methacrylate polymers and
copolymers, certain vinyl polymers and copolymers, certain polyvinyl
acetals, polycarbonates, polysulfones, polyetherimides, polyphenylene
oxides, etc. Types of low Tg resins useful as a binder include: certain
acrylate and methacrylate polymers and copolymers, certain vinyl polymers
and copolymers, certain polyvinyl acetals, polyesters, polyurethanes,
butadiene copolymers, cellulose esters, cellulose ethers, etc. Preferred
low Tg resins include poly(ethyl methacrylate) (Tg 70.degree. C.),
Elvacite.RTM. 2042 and 2045 resins. Preferred high Tg resins include
poly(methyl methacrylate) (Tg 110.degree. C.) and poly(styrene/methyl
methacrylate).
A useful resistivity range of the binder or binder combinations is about
10.sup.14 to 10.sup.20 ohm-cm, preferably 10.sup.14 to 10.sup.16 ohm-cm
range.
COMPOUNDS HAVING ETHYLENIC UNSATURATION
Any ethylenically unsaturated photopolymerizable or photocrosslinkable
compound can be used in the practice of this invention. Preferred
compounds are monomers which have at least two terminal ethylenically
unsaturated groups, e.g., di-, tri-, and tetraacrylates and methacrylates
such as ethylene glycol diacrylate, diethylene glycol diacrylate,
triethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate,
glycerol propoxylated triacrylate, ethylene glycol dimethacrylate,
1,2-propanediol dimethacrylate, 1,2,4-butanetriol trimethacrylate,
1,4-cyclohexanediol diacrylate, 1,4-benzenediol dimethacrylate,
pentaerythritol triacrylate, pentaerythritol trimethacrylate,
pentaerythritol tetramethacrylate, 1,3-propanediol diacrylate,
1,5-pentanediol dimethacrylate, trimethylolpropane triacrylate,
ethoxylated trimethylolpropane triacrylate, the bisacrylates and
bismethacrylate of polyethylene glycols of molecular weight 100-500,
tris-(2-hydroxyethyl)isocyanurate triacrylate, etc. Especially preferred
monomers are glyceryl propoxylated triacrylate, trimethylolpropane
triacrylate and mixtures thereof.
A monomer with a resistivity in the range of about 10.sup.5 to 10.sup.9
ohm-cm is particularly useful. Mixtures of monomers have been found to
enhance the improvement in environmental stability of the photohardenable
or photopolymerizable master. In this respect, blends of glycerol
propoxylated triacrylate and trimethylolpropane triacrylate in a 2:1 ratio
were found to give the best overall performance.
INITIATORS AND/OR INITIATOR SYSTEMS
A large number of free-radical generating compounds can be utilized in the
photopolymerizable compositions. Preferred initiator systems are
2,4,5-triphenylimidazolyl dimers with hydrogen donors, also known as the
2,2',4,4',5,5'-hexaarylbiimidazoles, or HABI's, and mixtures thereof,
which dissociate on exposure to actinic radiation to form the
corresponding triarylimidazolyl free radicals. HABI's and use of
HABI-initiated photopolymerizable systems for applications other than for
electrostatic uses have been previously disclosed in a number of patents.
These include: Chambers, U.S. Pat. No. 3,479,185, Chang et al., U.S. Pat.
No. 3,549,367, Baum and Henry, U.S. Pat. No. 3,652,275, Cescon, U.S. Pat.
No. 3,784,557, Dueber, U.S. Pat. No. 4,162,162, Dessauer, U.S. Pat. No.
4,252,887, Chambers et al., U.S. Pat. No. 4,264,708, Wade et al. U.S. Pat.
No. 4,410,621, and Tanaka et al., U.S. Pat. No. 4,459,349, the disclosures
of which are incorporated herein by reference. Useful
2,4,5-triarylimidazolyl dimers are disclosed in Baum and Henry, U.S. Pat.
No. 3,652,275 column 5, line 44 to column 7, line 16, the disclosure of
which is incorporated herein by reference. Any 2-o-substituted HABI
disclosed in the prior patents can be used in this invention.
The HABI's can be represented by the general formula
##STR7##
where the R's represent aryl, e.g., phenyl, naphthyl, radicals. The
2-o-substituted HABI's are those in which the aryl radicals at the 2- and
2'-positions are orthosubstituted or with polycyclic condensed aryl
radicals. The other positions on the aryl radicals can be unsubstituted or
carry any substituent which does not interfere with the dissociation of
the HABI upon exposure or adversely affect the electrical or other
characteristics of the photopolymer system.
Preferred HABI's are 2-o-chlorosubstituted hexaphenylbiimidazoles in which
the other positions on the phenyl radicals are unsubstituted or
substituted with chloro, methyl or methoxy. The most preferred initiators
include: 2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)imidazole dimer,
1,1'-biimidazole, 2,2-bis(o-chlorophenyl)-4,4,'5,5'-tetraphenyl
biimidazole, 2,5-bis(o-chlorophenyl)-4,-[3,4-dimethoxyphenyl]-imidazole
dimer, and
2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)biimidazol
e, each of which is typically used with a hydrogen donor or chain transfer
agent described below.
Photoinitiators that are also useful in the photohardenable composition in
place of the HABI type photoinitiators include: the substituted or
unsubstituted polynuclear quinones, aromatic ketones, and benzoin ethers.
Examples of such other photoinitiators are quinones, for example,
9,10-anthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone,
2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone,
octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone,
1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-methyl-1,4-naphthoquinone,
2,3-dichloronaphthoquinone,
1,4-dimethylanthraquinone,2,3-dimethylanthraquinone,
2-phenylanthraquinone, 2,3-diphenylanthraquinone, sodium salt of
anthraquinone .alpha.-sulfonic acid, 3-chloro-2-methylanthraquinone,
retenequinone, 7,8,9,10-tetrahydronaphthacenequinone,
1,2,3,4-tetrahydrobenz(a) anthracene-7,12-dione; aromatic ketones, for
example, benzophenone, Michler's ketone,
4,4'-bis(dimethylamino)benzophenone; 4,4'-bis(diethylamino)benzophenone,
4-acryloxy-4'-diethylaminobenzophenone,
4-methoxy-4'-dimethylaminobenzophenone, xanthones, thioxanthones; and
benzoin ethers, for example, benzoin methyl and ethyl ethers. Still other
photoinitiators which are also useful, are described in Plambeck U.S. Pat.
No. 2,760,863 and include vicinal ketaldonyl alcohols, such as benzoin,
pivaloin, acyloin ethers, .alpha.-hydrocarbonsubstituted aromatic
acyloins, including .alpha.-methylbenzoin, .alpha.-allylbenzoin and
.alpha.-phenylbenzoin. Additional systems include .alpha.-diketones with
amines as disclosed in Chang, U.S. Pat. No. 3,756,827, and benzophenone
with p-dimethylaminobenzaldehyde or with esters of p-dimethylaminobenzoic
acid as disclosed in Barzynski et al., U.S. Pat. No. 4,113,593. The
disclosures of the above patents are incorporated herein by reference.
Redox systems, especially those involving dyes, e.g., Rose Bengal,
2-dibutylaminoethanol, are also useful in the practice of this invention.
Photoreducible dyes and reducing agents such as those disclosed in U.S.
Pat. Nos. 2,850,445; 2,875,047; 3,074,974; 3,097,096; 3,097,097;
3,145,104; and 3,579,339; as well as dyes of the phenazine, oxazine, and
quinone classes can be used to initiate photopolymerization, the
disclosures of which are incorporated herein by reference. A useful
discussion of dye sensitized photopolymerization can be found in "Dye
Sensitized Photopolymerization" by D. F. Eaton in Adv. in Photochemistry,
Vol. 13, D. H. Volman, G. S. Hammond, and K. Gollinick, eds.,
Wiley-Interscience, New York, 1986, pp. 427-487.
ACIDIC ADDITIVE
The acidic additive is selected from the group consisting essentially of:
(1) compounds of the general formula:
R--NH--R'
where R is R.sup.1 --SO.sub.2,
##STR8##
R' is H, acyl, alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl,
##STR9##
halogen or heterocyclic groups; R and R' when taken together may form a
heterocyclic ring; R.sup.1, R.sup.2 and R.sup.3 may be the same or
different and are alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, acyl, halogen or heterocyclic
groups.
(2) phosphonic acids of the general formula:
##STR10##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl, substituted aryl, halogen or heterocyclic
groups; and
(3) polybasic carboxylic acids having at least two acid groups.
Compounds of Group 1 include: sulfonamides and imides, sulfonylureas,
carboximides, and phosphonamides.
Sulfonamides and imides are represented by the formula:
R.sup.1 --SO.sub.2 --NH--R'
where R.sup.1 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl or substituted aryl substituted with alkyl, e.g.,
1 to 10 carbon atoms, alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl,
Br, I; amino, carboxylic ester, etc.; and R' is H, acyl, alkyl of 1 to 12
carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl or
substituted aryl substituted as described above for R.sup.1. Sulfonamides
are illustrated in the examples by A3, A4, A5, A6, and A7. Sulfonamides
and imides are described in the following publications:
"Sulfonamides and Allied Compounds" by E. H. Northey, 1948, Reinhold
Publishing Corp., N.Y.
"Sulfonamides" Encyclopedia of Chemical Technology, Volume 2, Kirk-Othmer,
pp. 795-808, 1978, Wiley-Interscience, N.Y.
Sulfonylureas are represented by the formula:
##STR11##
where R.sup.1 and R' may be the same or different and are alkyl of 1 to 12
carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl or
substituted aryl substituted with alkyl, e.g., 1 to 10 carbon atoms,
alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl, Br, I; amino, carboxylic
ester, etc.; and heterocyclic 5- or 6-membered rings containing N, 0, S,
Se, P, As, etc., in the ring. Suitable sulfonylureas and their method of
preparation are described in U.S. Pat. Nos. 4,127,405, 4,383,113,
4,394,506, 4,420,325, 4,435,206, 4,478,635, 4,479,821, 4,481,029,
4,514,212, 4,789,393, 4,810,282, and EP-A-87,780. Sulfonylurea is
illustrated in the examples by A11.
Carboximides are represented by the formula:
##STR12##
where R.sup.1 and R' may be the same or different and are alkyl of 1 to 12
carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl or
substituted aryl substituted with alkyl, e.g., 1 to 10 carbon atoms,
alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl, Br, I; amino, carboxylic
ester, etc.; and heterocyclic 5- or 6-membered rings) containing N, 0, S,
Se, P, As, etc., in the ring. R.sup.1 and R' when taken together may form
heterocyclic 5- or 6- membered rings or condensed rings. Carboximides are
illustrated in the examples by A9 (acyclic), A8 and A10 (cyclic). Other
useful carboximide compounds include:
##STR13##
Phosphonamides are represented by the formula:
##STR14##
where R.sup.1, R' and R.sup.2 may be the same or different and are alkyl
of 1 to 12 carbon atoms, aryl of 6 to 30 carbon atoms, substituted alkyl
or substituted aryl substituted with alkyl, e.g., 1 to 10 carbon atoms,
alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl, Br, I; amino, carboxylic
ester, etc.; halogen, or heterocyclic 5- or 6-membered) containing N, O,
S, Se, P, As, etc., in the ring. Phosphonamide is illustrated in the
examples by A13. Additional phosphonamide compounds are derived from
phosphonic acids described in the following paragraph.
Phosphonic acid is represented by the formula:
##STR15##
where R.sup.4 is alkyl of 1 to 12 carbon atoms, aryl of 6 to 30 carbon
atoms, substituted alkyl or substituted aryl substituted with alkyl, e.g.,
1 to 10 carbon atoms, alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl,
Br, I; amino, carboxylic ester, etc.; halogen, and heterocyclic 5- or 6-
membered rings containing N, 0, S, Se, P, As, etc. in the ring. Phosphonic
acid is illustrated in the examples by A12. Additional phosphonic acids
are described in the following publications:
"Organophosphorus Compounds" by G. M. Kosolapoff, pp. 148-170, 1950, John
Wiley and Sons, Inc., N.Y.
"Organophosphorus Chemistry", Specialist Periodical Reports, Volumes 1 to
19,1970 to 1988, The Chemical Society, Burlington House, London.
Polybasic carboxylic acids having at least 2 acid groups, which are more
acidic than monobasic acids, are represented by the formula:
HO.sub.2 C--R.sup.5 --CO.sub.2 H
wherein R.sup.5 is aliphatic of 0 to 12 carbon atoms (saturated or
unsaturated substituted or unsubstituted), aryl of 6 to 30 carbon atoms,
substituted alkyl and substituted aryl substituted with alkyl, e.g., 1 to
10 carbon atoms, alkoxy of 1 to 6 carbon atoms, halogen, e.g., Cl, Br,
I;amino, carboxylic ester, etc. Suitable polybasic acids include oxalic,
malonic, citric, tartaric, maleic, fumaric, trimellitic, phthalic,
diphenic, pyromellitic, naphthalene dicarboxylic, etc. Polybasic acids are
illustrated in the examples by A14, A15, A16 and A17. Additional
polybasic carboxylic acids are described in the following references:
"Practical Organic Chemistry" by A. I. Vogel, pp. 489-495 and 751-779,
1957, John Wiley & Sons, N.Y.
"Chemistry of Organic Compounds" by C. R. Noller, pp. 870-891, 1965, W. B.
Saunders Company, Philadelphia.
ADDITIONAL COMPONENTS
Sensitizers
Sensitizers useful with these photoinitiators include those disclosed in
U.S. Pat. Nos. 3,554,753; 3,563,750; 3,563,751; 3,647,467; 3,652,275;
4,162,162; 4,268,667; 4,351,893; 4,454,218; 4,535,052; and 4,565,769, the
disclosures of which are incorporated hereby by reference.
A preferred group of visible sensitizers include the
bis(p-dialkylaminobenzylidene) ketones disclosed in Baum and Henry, U.S.
Pat. No. 3,652,275 and the arylyidene aryl ketones disclosed in Dueber,
U.S. Pat. No. 4,162,162, as well as in U.S. Pat. Nos. 4,268,667 and
4,351,893, the disclosure of each being incorporated herein by reference.
These compounds extend the sensitivity of the initiator system to visible
wavelengths where lasers emit. Particularly preferred sensitizers are:
2-{9'(2',3',6',7'-tetrahydro-1H,5H-benzo[i,j]-quinol-ylidene)}-5,6-dimetho
xy-1-indanone (DMJDI), and
2,5Bis{9'-(2',3',6',7'-tetrahydro-lH,5H-benzo[i,j]quinolylidene)}cyclopent
anone (JAW).
CHAIN TRANSFER AGENTS
Any chain transfer agent, or hydrogen donor, identified in the prior
patents for use with HABI-initiated photopolymerizable systems can be
used. For example, Baum and Henry, U.S. Pat. No. 3,652,275 discloses
N-phenylglycine, 1,1-dimethyl-3,5-diketocyclohexane, and organic thiols
such as 2-mercaptobenzothiazole, 2-mercaptobenzoxazole,
2-mercaptobenzimidazole, pentaerythritol tetrakis(mercaptoacetate),
4-acetamidothiophenol, mercaptosuccinic acid, dodecanethiol, and
beta-mercaptoethanol, 2-mercaptoethane sulfonic acid,
1-phenyl-4H-tetrazole-5-thiol, 6-mercaptopurine monohydrate,
bis-(5-mercapto-1,3,4-thiodiazol-2-yl, 2-mercapto-5-nitrobenzimidazole,
and 2-mercapto-4-sulfo-6-chlorobenzoxazole, the disclosure of which is
incorporated by reference. Also useful are various tertiary amines known
in the art. Other hydrogen donor compounds useful as chain transfer agents
in photopolymerizable compositions include various other types of
compounds, e.g., (a) ethers, (b) esters, (c) alcohols, (d) compounds
containing allylic or benzylic hydrogen cumene, (e) acetals, and (f)
aldehydes, as disclosed in column 12, lines 18 to 48, of MacLachlan, U.S.
Pat. No. 3,390,996, the disclosure of which is incorporated herein by
reference. The preferred chain transfer agents are 2-mercaptobenzoxazole
(2-MBO) and 2-mercaptobenzothiazole (2-MBT).
OTHER ADDITIONAL COMPONENTS
The photohardenable compositions may also contain other ingredients which
are conventional components used in photopolymerizable systems. Such
components include: thermal stabilizers or thermal polymerization
inhibitors, photoinhibitors, antihalation agents, UV absorbers, release
agents, colorants, surfactants, plasticizers, electron donors, electron
acceptors, charge carriers, etc.
Normally a thermal stabilizer or thermal polymerization inhibitor will be
present in small quantities, e.g., <0.1%, to increase stability in the
storage of the photopolymerizable composition. Useful thermal stabilizers
or inhibitors include: hydroquinone, phenidone, p-methoxyphenol, alkyl and
aryl-substituted hydroquinones and quinones, tert-butyl catechol,
pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprous
chloride, 2,6-di-tert-butyl p-cresol, phenothiazine, pyridine,
nitrobenzene, dinitrobenzene, p-toluquinone and chloranil. The dinitroso
dimers described in Pazos, U.S. Pat. No. 4,168,982 are also useful, the
disclosure of which is incorporated. A preferred stabilizer is TAOBN,
i.e., 1,4,4-trimethyl-2,3-diazobicyclo-(3.2.2)-non-2-ene-N,N-dioxide.
Photoinhibitors are disclosed in Pazos U.S. Pat. No. 4,198,242, the
disclosure of which is incorporated herein by reference. A specific
photoinhibitor is
1-(2'-nitro-4',5'-dimethoxy)phenyl-1-(4-t-butylphenoxy)ethane.
Antihalation agents useful in the photohardenable compositions include
known antihalation dyes.
Ultraviolet radiation absorbing materials useful in the invention are also
disclosed in U.S. Pat. No. 3,854,950, the disclosure of which is
incorporated herein by reference.
Compounds present in the composition as release agents are described in
Bauer, U.S. Pat. No. 4,326,010, the disclosure of which is incorporated
herein by reference. A specific release agent is polycaprolactone.
Suitable plasticizers include: triethylene glycol, triethylene glycol
dipropionate, triethylene glycol dicaprylate, triethylene glycol
bis(2-ethyl hexanoate), tetraethylene glycol diheptanoate, polyethylene
glycol, diethyl adipate, tributyl phosphate, etc. Other plasticizers that
yield equivalent results will be apparent to those skilled in the art.
Suitable electron donors and acceptors are disclosed in Blanchet-Fincher et
al., U.S. Pat. No. 4,849,314, the disclosure of which is incorporated
herein by reference.
Suitable charge carriers are disclosed in Blanchet-Fincher et al. U.S. Pat.
No. 4,818,660, the disclosure of which is incorporated herein by
reference.
Suitable leuco dyes include: tris-(o-methyl-p-diethylaminophenyl)methane,
4,4'-benzylidene bis (N,N-dimethylaniline) as disclosed in
Blanchet-Fincher et al. U.S. Pat. No. 4,818,660, column 8, lines 26-34,
the disclosure of which is incorporated herein by reference.
PROPORTIONS
In general, the components should be used in the following approximate
proportions: binder 40-70%, preferably 50-65%; monomer 15-40%, preferably
20-35%, initiator 1-20%, preferably 1-8%, acidic additive 1-10%,
preferably 2-6%, and chain transfer agent or hydrogen donor 0-10%,
preferably 0.1-4%. These are weight percentages based on total weight of
the photopolymerizable system.
The preferred proportions depend upon the particular compounds selected for
each component and the application for which the photohardenable
composition is intended. For example, a high conductivity monomer can be
used in smaller amount than a low conductivity monomer, since the former
will be more efficient in eliminating charge from unexposed areas.
The amount of HABI photoinitiator will depend upon film speed requirement.
Photohardenable compositions with HABI content above 10% provide films of
high sensitivity (high speed) and can be used with laser imaging in
recording digitized information, as in digital color proofing. Such films
are the subject of Legere U.S. Ser. No. 07/284,891, filed Dec. 13, 1988,
now U.S. Pat. No. 4,911,999, the disclosure of which is incorporated
herein by reference. For analog applications, e.g., exposure through a
negative, film speed requirement depends upon mode of exposure. Slow speed
films are acceptable for analog applications.
COATING/SUBSTRATES
The photohardenable layer is prepared by mixing the ingredients of the
photopolymerizable composition in a solvent, such as methylene chloride,
usually in the weight ratio of about 15:85 to 25:75 (solids to solvent),
coating on a substrate, and evaporating the solvent. Coatings should be
uniform and should have a thickness of 3 to 20 .mu.m, preferably 7 to 12
.mu.m, when dry. Dry coating weight should be about 30 to 200 mg/dm.sup.2,
preferably 80 to 150 mg/dm.sup.2. A coversheet, e.g., polyethylene,
polypropylene, polyethylene terephthalate, etc. is preferably placed over
the photohardenable layer after the solvent evaporates for protection.
The substrate should be uniform and free of defects such as pinholes,
bumps, and scratches. It can be a support, such as paper, glass, synthetic
resin and the like, which has been coated by vapor deposition or
sputtering chemical deposition on one or both sides with a metal,
conductive metal oxide, or metal halide, such as aluminized polyethylene
terephthalate; or a conductive paper or polymeric film. The coated
substrate mounted directly on a conductive support can be mounted directly
on the printing device.
Alternatively, the substrate can be a non-conducting film, preferably a
release film such as polyethylene or polypropylene. After removal of the
protective cover sheet, the photohardenable layer can then be laminated to
a conductive support on the printing device with the tacky,
photohardenable layer adjacent to the support. The substrate then acts as
a coversheet which is removed after exposure but prior to charging.
As another alternative, the conductive support may be a metal plate, such
as aluminum, copper, zinc, silver or the like; or a support which has been
coated with a polymeric binder containing a metal, conductive metal oxide,
metal halide, conductive polymer, carbon black or other conductive filler.
ELECTRICAL CHARACTERISTICS
To evaluate the photopolymerizable compositions, voltage is measured on the
unexposed photohardenable layer as a function of time using standard
conditions of charging and measurement.
The desired electrical properties of the photohardenable element are
dependent on the charge deposited on the photohardenable surface and the
electrical characteristics of the particular toner or developer system
employed. Ideally, at the time of contact, e.g., with a developer
dispersion, the voltage in the exposed areas (Vexp) should be at least 10
V, preferably at least 100 V and even up to 400 V or higher, more than
that of the voltage in unexposed areas (Vunexp). Resistivity of the
exposed areas should be between about 10.sup.14 and 10.sup.17 ohm-cm.
Resistivity in the unexposed areas should be between 10.sup.12 and
10.sup.15 ohm-cm and the ratio of resistivity in exposed areas to
resistivity in unexposed areas should be at least 100. A typical time for
toner or developer application is between 1 and 5 seconds after charging.
EXPOSURE/CHARGING/TONING/TRANSFER
To provide the required conductivity differential, exposure must be
sufficient to cause substantial polymerization in exposed areas. Exposing
radiation can be modulated by either digital or analog means. Analog
exposure utilizes a line or halftone negative or other pattern interposed
between the radiation source and photohardenable layer of the master. For
analog exposure an ultraviolet light source is preferred, since the
photopolymerizable system is more sensitive to shorter wavelength
radiation. Digital exposure may be carried out by a computer controlled,
light-emitting, e.g., visible light emitting, laser which scans the film
in raster fashion. For digital exposure a high speed film, i.e., one which
contains a high level of HABI and which has been sensitized to longer
wavelengths with a sensitizing dye, is preferred. Electron beam exposure
can be used, but is not preferred because of the expensive equipment
required.
The preferred electrostatic charging means is corona discharge. Other
charging methods include: discharge of a capacitor, negative corona
discharge, shielded corotron, scorotron, etc.
Any electrostatic toner or developer and any method of developer
application can be used. Liquid developers, i.e., a suspension of
pigmented resin toner particles in a nonpolar dispersant liquid present in
major amount, are preferred. The liquids normally used are Isopar.RTM.
branched-chain aliphatic hydrocarbons (sold by Exxon Corporation) which
have a Kauri-butanol value of less than 30. These are narrow high-purity
cuts of isoparaffinic hydrocarbon fractions with the following boiling
ranges Isopar.RTM.-G, 157.degree.-176.degree. C., Isopar.RTM.-H
176.degree.-191.degree. C., Isopar.RTM.-K 177.degree.-197.degree. C.,
Isopar.RTM.-L 188.degree.-206.degree. C., Isopar.RTM.-M
207.degree.-254.degree. C., Isopar.RTM.-V 254.degree.-329.degree. C. The
liquid developers may contain various adjuvants which are described in:
Mitchell, U.S. Pat. Nos. 4,631,244, 4,663,264, and 4,734,352; Taggi, U.S.
Pat. No. 4,670,370; Larson and Trout, U.S. Pat. No. 4,681,831; El-Sayed
and Taggi, U.S. Pat. No. 4,702,984; Larson, U.S. Pat. No. 4,702,985; and
Trout, U.S. Pat. No. 4,707,429. The liquid electrostatic developers can be
prepared as described in Larson U.S. Pat. No. 4,760,009. The disclosures
in these patents are incorporated herein by reference.
Also present in the liquid electrostatic developers are thermoplastic
resins, having an average particle size of less than 10 .mu.m, e.g., as
determined by the Horiba CAPA-500 centrifugal particle analyzer, Horiba
Instruments, Inc., Irvine, Calif., and Malvern 3600E Particle Sizer,
Malvern, Southborough, Mass., which are, for example, copolymers of
ethylene (80 to 99.9%) with acrylic acid, methacrylic acid, or alkyl
esters, where alkyl is 1 to 5 carbon atoms, of acrylic or methacrylic acid
(20 to 0.1%), e.g., an ethylene/methacrylic acid (89:11) copolymer having
a melt index at 190.degree. C. of 100. Preferred nonpolar liquid soluble
ionic or zwitterionic components present in such developers, for example,
are lecithin and Basic Barium Petronate.RTM. oil-soluble petroleum
sulfonate, Witco Chemical Corp., New York, N.Y.
Many of the monomers useful in the photohardenable composition described
above are soluble in these Isopar.RTM. hydrocarbons, especially in
Isopar.RTM.-L. Consequently, repeated toning with Isopar.RTM.-based
developers to make multiple copies can deteriorate the electrical
properties of the photohardenable master by extraction of monomer from
unexposed areas. The preferred monomers are relatively insoluble in
Isopar.RTM. hydrocarbons, and extended contact with these liquids does not
unduly deteriorate photohardenable layers made with these monomers.
Photohardenable electrostatic masters made with other, more soluble
monomers can still be used to make multiple copies, using liquid developer
having a dispersant with less solvent action.
Representative dry electrostatic toners that may be used include: Kodak
Ektaprint K, Hitachi HI-Toner HMT-414, Canon NP-350F toner, Toshiba T-50P
toner, etc. The invention is not limited by these toners.
After developing the toned image is transferred to a receptor surface, such
as paper, for the preparation of a proof. Other receptors include:
polymeric film, cloth, etc. For making integrated circuit boards, the
transfer surface can be an insulating board on which conductive circuit
lines can be printed by the transfer, or the surface can be an insulating
board covered with a conductor, e.g., a fiber glass board covered with a
copper layer, on which a resist is printed by transfer.
Transfer is accomplished by electrostatic or other means, e.g., by contact
with an adhesive receptor surface. Electrostatic transfer can be
accomplished in any known manner, e.g., by placing the receptor surface,
e.g., paper, in contact with the toned image. A tackdown roll or corona,
when held at negative voltages, will press the two surfaces together
assuring intimate contact. After tackdown, a positive corona discharge is
applied to the backside of the paper to drive the toner particles off the
electrostatic master onto the paper.
INDUSTRIAL APPLICABILITY
The photohardenable electrostatic master having improved charge decay
characteristics is particularly useful in the graphic arts field,
especially in the area of color proofing wherein the proofs prepared
duplicate the images produced by printing. This is accomplished by
controlling the gain of the reproduced halftone dots through control of
the electrical conductivity of the exposed and unexposed areas of the
photohardenable electrostatic master. Since the voltage retained by the
halftone dots is almost linearly related to the percent dot area, the
thickness of the liquid electrostatic developer will be constant
everywhere on the image, independent of the particular dot pattern to be
developed. The photohardenable electrostatic master has improved adhesion
of the photohardenable layer to the substrate over previous
photohardenable electrostatic masters. Other uses for the photohardenable
master include preparation of printed circuit boards, resists, soldermask,
photohardenable coatings, etc.
EXAMPLES
The advantageous properties of this invention can be observed by reference
to the following examples which illustrate, but do not limit, the
invention. The parts and percentages are by weight.
Glossary
BINDERS
B1 Poly(styrene/methyl methacrylate) 70/30 copolymer
B2 Poly (methyl methacrylate)
B3 Poly (ethyl methacrylate)
MONOMERS
M1 Ethoxylated trimethylolpropane triacrylate
M2 Glycerol propoxylated triacrylate
M3 Trimethylolpropane triacrylate
INITIATORS
IN 1 2,2',4,4'-tetrakis(o-chlorophenyl)-5,5'-bis(m,p-dimethoxyphenyl)
biimidazole (TCTM-HABI)
IN 2 Benzoin methyl ether
IN 3 2-Chloro-thioxanthenone
CHAIN TRANSFER AGENT
CT1 2-Mercaptobenzoxazole (2-MBO)
CT2 2-Mercaptobenzothiazole (2-MBT)
STABILIZER OR INHIBITOR
S1 1,4,4-Trimethyl-2,3-diazobicyclo-[3,2,2]-non-2-ene-N,N-dioxide
S2 1-(2'-Nitro-4',5'-dimethoxyphenyl)-1-(4-t-butylphenoxy)ethane
(.alpha.-methyl-BPE)
LEUCO DYES
LD1 Tris-(o-methyl-p-diethylaminophenyl) methane
LD2 Leuco Malachite Green, 4,4'-benzylidenebis(N,N-dimethylaniline)
ACIDIC ADDTTIVES
A1 Acetic acid (Control)
A2 p-Toluic acid (Control)
A3 Benzenesulfonamide
A4 Ketjenflex.RTM.9 S, mixture of o, p-toluenesulfonamide
A5 Alpha-toluenesulfonamide
A6 p-(p-Toluenesulfonamido) diphenylamine
A7 Saccharin or benzoic sulfonimide
A8 Phthalimide
A9 Diacetamide
A10 Parabanic acid
A11 N-(2-methoxy-4-methyl-S-triazinyl)-N'-(o-chlorobenzenesulfonyl) urea
A12 Benzene phosphonic acid
A13 Phenyl N-phenylphosphonamido chloridate
A14 Phthalic acid
A15 Maleic acid
A16 Diphenic acid
A17 Citric acid
Except as indicated otherwise, the following procedures were used in all
examples.
A solution containing about 80 parts methylene chloride and 20 parts of
solids was coated onto a 0.004 inch (0.0102 cm) aluminized polyethylene
terephthalate support. After the film had been dried at
60.degree.-95.degree. C. to remove the methylene chloride, a 0.00075 inch
(0.0019 cm) polypropylene cover sheet was laminated to the dried layer.
The coating weights varied from 80 to 150 mg/dm.sup.2. The film was then
wound on rolls until exposure and development occurred.
In order to test the image quality of each photopolymerizable composition,
the photopolymerizable layer was exposed, charged, and toned with magenta
toner, and the image transferred to paper as described below. In all cases
"magenta toner" refers to the standard magenta toner used to form a four
color proof described below. The evaluation of image quality was based on
dot range and dot gain on paper. The standard paper is 60 lbs
Solitaire.RTM. paper, offset enamel text, Plainwell Paper Co., Plainwell,
Mich. However, the variety of papers tested included: 60 lbs Plainwell
offset enamel text, 70 lbs Plainwell offset enamel text, 150 lbs white
regal Tufwite.RTM. Wet Strength Tag, 60 lbs White LOE Gloss Cover, 70 lbs
white Flokote.RTM. Text, 60 lbs white all purpose lith, 110 lbs white
Scott index, 70 lbs white Nekoosa Vellum Offset and 80 lbs white Sov.RTM.
text. Results indicated that, although the process can be used with any
paper, the trapping of ink varies with the fibrillar nature of the paper
in use.
Dot gain or dot growth versus dot size is a standard measure of how
tolerances between a proof and a press proof are determined. The dot gains
were measured using designed patterns called Brunner targets which are
available from System Brunner USA, Inc., Rye, N.Y. Typically desired dot
gains for graphic arts applications are in the range of 15 to 22% at
midtone. The dot range was easily tested using URGA targets, Graphic Arts
Technical Foundation, Pittsburgh, Pa., that include 0.5% highlight dots to
99.5% shadow dots and in a 133 lines/mm screen that includes 4 .mu.m
highlights and shadow microlines. Typically desired dot ranges for graphic
arts applications are in the range of 2 to 98%.
The photohardenable electrostatic master was first exposed through a
separation negative using a Douthitt Option X Exposure Unit (Douthitt
Corp., Detroit, Mich.), equipped with a model TU 64 Violux.RTM.5002 lamp
assembly (Exposure Systems Corp., Bridgeport, Conn.) and model No. 5027
photopolymer type lamp. Exposure times varied from 1-100 seconds depending
on the formulation. The exposed master was then mounted on a drum surface.
SWOP (Specification Web Offset Publications) density in the solid regions
was obtained by charging the fully exposed regions of the
photopolymerizable layer of the electrostatic master to 100 to 200 V. The
charged latent image was then developed with a liquid electrostatic
developer, using a two roller toning station and the developer layer
properly metered. The developing and metering stations were placed a 5 and
6 o'clock respectively. The toner image was corona transferred onto paper
using 10-150 microamps transfer corona and 4.35 to 4.88 kV, and -2.5 to
-8.0 kV tackdown roll voltage at a speed of 2.2 inches/second (5.59
cm/second) and fused in an oven for 10 seconds at 100.degree. C.
A four color proof is obtained by following the steps described below.
First, complementary registration marks are cut into the
photopolymerizable layers of the electrostatic masters prior to exposure.
Masters for each of the four color separations are prepared by exposing
four photopolymerizable elements having coversheets to one of the four
color separation negatives corresponding to cyan, yellow, magenta and
black colors. Each of the four photopolymerizable layers is exposed for
about 3 seconds using the Douthitt Option X Exposure Unit described above.
The visible radiation emitted by this source is suppressed by a UV light
transmitting, visible light absorbing Kokomo.RTM. glass filter (No. 400,
Kokomo Opalescent Glass Co., Kokomo, Ind.). The cover sheets are removed,
and each master is mounted on the corresponding color module drum, in a
position assuring image registration of the four images as they are
sequentially transferred from each master to the receiving paper. The
leading edge clamps are also used to ground the backplane of the
electrically conductive substrate to the drum. The masters are stretched
by spring loading the trailing edge assuring that each lays flat against
its drum.
Each module comprised a charging scorotron at 3 o'clock position, a
developing station at 6 o'clock, a metering station at 7 o'clock and a
cleaning station at 9 o'clock. The charging, developing, and metering
procedure is similar to that described above. The transfer station
consists of a tackdown roll, a transfer corona, paper loading, and a
positioning device that fixes the relative position of paper and master in
all four transfer operations.
In the preparation of the four-color proof the four developers, or toners,
have the following compositions:
______________________________________
INGREDIENTS AMOUNT (g)
______________________________________
BLACK
Copolymer of ethylene (89%) and
2,193.04
methacrylic acid (11%), melt
index at 190.degree. C. is 100, acid no. is 66
Sterling NF carbon black
527.44
Heucophthal Blue, G XBT-583D
27.76
Heubach, Inc., Newark, NJ
Basic Barium Petronate .RTM.,
97.16
Witco Chemical Corp., New York, NY
Aluminum tristearate, Witco 132
27.76
Witco Chemical Corp., New York, NY
L, non-polar liquid 188,670.0
having a Kauri-Butanol value
of 27, Exxon Corporation
CYAN
Copolymer of ethylene (89%) and
3,444.5
methacrylic acid (11%), melt
index at 190.degree. C. is 100, acid no. is 66
Ciba-Geigy Monarch Blue X3627
616.75
Dalamar .RTM. Yellow YT-858D Heubach, Inc.,
6.225
Newark, NJ
Aluminum tristearate, as described
83.0
in black developer
Basic Barium Petronate .RTM.
311.25
(Witco Chemical Corp.)
L as described in 292,987.0
black developer
MAGENTA
Copolymer of ethylene (89%) and
3973.47
methacrylic acid (11%), melt
index at 190.degree. C. is 100, acid no. is 66
Mobay RV-6700, Mobay Chemical Corp.,
1156.66
Haledon, NJ
Mobay RV-6713, Mobay Chemical Corp.
204.12
Haledon, NJ
Aluminum stearate S, 108.86
Witco Chemical Corp.
Basic Barium Petronate .RTM. ,
326.58
Witco Chemical Corp.
L as described in 378,876.0
black developer
YELLOW
Copolymer of ethylene (89%) and
1,824.75
methacrylic acid (11%), melt
index at 190.degree. C. is 100, acid no. is 66
Yellow 14 polyethylene flush,
508.32
Sun Chemical Co., Cincinnati, OH
Aluminum tristearate, as described
46.88
in black developer
Basic Barium Petronate .RTM. ,
59.5
Witco Chemical Corp.
L as described 160,191.0
in black developer
______________________________________
First, the cyan master is charged, developed and metered. The transfer
station is positioned and the toned cyan image transferred onto the paper.
After the cyan transfer is completed, the magenta master is corona
charged, developed and metered, and the magenta image transferred, in
registry, on top of the cyan image. Afterwards, the yellow master is
corona charged, developed, and metered, and the yellow image is
transferred on top of the two previous images. Finally the black master is
corona charged, developed, metered, and the toned black image transferred,
in registry, on top of the three previously transferred images. After the
procedure is completed, the paper is carefully removed from the transfer
station and the image fused for 15 seconds at 100.degree. C.
The parameters used for preparation of the proof are: drum speed, 2.2
inches/second (5.588 cm/second); grid scorotron voltage, 100 to 400 V;
scorotron current 200 to 1000 microamps (5.11 to 6.04 kV); metering roll
voltage, 20 to 200 V; tackdown roll voltage, -2.5 to -8.0 kV; transfer
corona current, 10 to 150 microamps (4.35 to 4.88 kV); metering roll
speed, 4 to 8 inches/second (10.16 to 20.32 cm/second.); metering roll
gap, 0.002 to 0.005 inch (0.51 to 0.0127 mm); developer conductivity 12 to
30 picomhos/cm; developer concentration, 1 to 2.0% solids.
To test for backtransfer, the exposed element was mounted on a drum
surface. The charged latent image was developed with the magenta toner
used in the preparation of the four-color proof. The charging corona
voltage and current were adjusted to give SWOP density in the solid areas.
Standard conditions were 200 to 300 V in the scorotron grid, 550 uA
charging corona current.
After the transfer of the first image was completed, the photohardenable
element (electrostatic master) was tested for backtransfer latitude in
three sequential charging, developing and transfer cycles as follows: the
paper, with a wet image on top, was carefully placed in the transfer
position. The leading edge of the photohardenable element and the wet
image on paper were aligned one inch (2.54 cm) apart and with both the
leading and trailing edges of the paper held away from the photohardenable
element. The electrostatic master was cleaned and the second charging,
developing and transferring cycle started. A second toner layer on top of
the original image was thus obtained. The second image transfer efficiency
and the extent of backtransfer of the previous image were evaluated by an
operator standing near the exit of the transfer zone. After the second
transfer was completed the procedure was repeated a third and a fourth
time always checking for backtransfer. These four passes simulate the
actual making of a four-color proof in which the image first developed is
subjected to the transfer field three more times before the proof is
completed. The above procedure was repeated for at least two transfer
conditions where the transfer corona current varied from 10 to 50
microamps and the tackdown roll voltage from -2.5 to -8.0 kV (standard
conditions: 30 uA and -3.0 kV). The presence of acidic additives in the
photohardenable layer as illustrated in the following examples alleviated
backtransfer under a wide range of operating conditions. A photohardenable
layer that would not backtransfer under these conditions should be
suitable as an electrostatic master in a multiple color system.
EXAMPLE 1
Solutions of photopolymerizable compositions were prepared containing 80
parts of methylene chloride and 20 parts of solids. The solids comprised
monomer or combination of monomers, binder or combinations of binders,
initiator, acidic additive and chain transfer agent. The solutions were
coated on 0.004 inch (0.0102 cm) aluminized polyethylene terephthalate
support and a 0.00075 inch (0.001905 cm) polypropylene cover sheet was
present. The coating weights varied from 80 to 150 mg/cm.sup.2 or an
approximate thickness of 7 .mu.m to 12 .mu.m in sample thickness.
The photopolymerizable layer for each element had the following composition
wherein the amounts are in parts.
TABLE 1
__________________________________________________________________________
COMPOSITIONS (PARTS)
SAMPLE
B1
M1 IN1
CT1
A3
A4
A5
A6
A7
A8
A10
A12
A13
A14
A15
__________________________________________________________________________
1* 58
28 5 3
2 58
28 5 3 4
3 58
28 5 3 3
4 58
28 5 3 3
5 58
28 5 3 4
6 58
28 5 3 4
7 58
28 5 3 4
8 58
28 5 3 4
9 58
28 5 3 4
10 58
28 5 3 4
11 58
28 5 3 3
12 58
28 5 3 3
__________________________________________________________________________
All contain 0.03 part of S1 and 3 parts LD1.
*Control
Results are shown in Table 2 below.
TABLE 2
______________________________________
BACKTRANSFER
SAM- 10 uA, -2.5 kV
30 uA, -3.5 kV
50 uA, -4.5 kV
PLE 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd
______________________________________
1* Y Y Y Y Y Y Y Y Y
2 N N N N N N N L L
3 N N L N N L N N L
4 N L L L L L L L L
5 P L L L L L L L L
6 N N N N N N N N N
7 L L L N N N L L L
8 N N N N N N N N N
9 N N N N N N N N N
10 N N N N N N N N N
11 N N N N N N N N N
12 N N N N N N N N N
______________________________________
*Control
The abbreviations are defined below:
1st is the second image transferred.
2nd is the third image transferred.
3rd is the fourth image transferred.
N is substantially no backtransfer.
L is low backtransfer.
Y is fair backtransfer.
P is poor transfer efficiency.
EXAMPLE 2
Thirteen photopolymerizable elements were prepared and tested as described
in Example 1 with the following exceptions: the photopolymerizable layer
for each element had the composition shown in Table 3 below. Results are
shown in Table 4 below.
TABLE 3
__________________________________________________________________________
COMPOSITIONS (PARTS)
SAMPLE
B1
B2
B3
M1 M2 M3 IN1
CT1
A3
A4
A7
A9
A11
A12
A17
LD1
__________________________________________________________________________
13* 57 27 5 3 3
14 57 27 5 3 5 3
15 57 27 5 3 8 3
16 57 27 5 3 5 3
17 57 27 5 3 3 3
18 57 27 5 3 5 3
19 57 27 5 3 2.5 3
20 21
42
25 3 2 5 3
21 58 20 9 3 3 5 4
22 58 29 3 3 5 4
23 56 29 3 3 5 4
24 63
24 3 3 5 3
25 59 28 3 2 5 3
__________________________________________________________________________
All contain 0.03 part of TAOBN thermal inhibitor.
*Control
TABLE 4
______________________________________
BACKTRANSFER
50 uA, -7.0 kV
50 uA, -8.0 kV
SAMPLE 1st 2nd 3rd 1st 2nd 3rd
______________________________________
13* Y Y Y Y Y Y
14 N N N N N N
15 N N N N N N
16 N N N N N N
17 N N N N N N
18 N N N N N N
19 N N N N N N
20 N N N N N N
21 N N N N N N
22 N N N N N N
23 N N N N N N
24 N N N N N N
25 N N N N N N
______________________________________
*Control
EXAMPLE 3
Eight photopolymerizable elements were prepared and tested as described in
Example 1 with the following exceptions: the photopolymerizable layer for
each element had the composition shown in Table 5 below. Results are also
shown in Table 6 below.
TABLE 5
__________________________________________________________________________
COMPOSITIONS (PARTS)
SAMPLE
B1
M1 IN1
IN2
IN3
LD1
LD2
A3
A7
CT1
CT2
S1
__________________________________________________________________________
26* 58
28 5 3 0.03
27* 58
31 5 3 3 0.03
28 58
26 5 4 4 3 0.03
29 58
29 5 2.5 2.5 3 0.03
30 59
29 5 3 4
31 59
29 5 3 4
32 59
28 3 3 5 3
33 58
27 5 3 4 3
__________________________________________________________________________
*Controls
TABLE 6
______________________________________
BACKTRANSFER
SAM- 30 uA, -3.5 kV
50 uA, -5.0 kV
50 uA, -7.0 kV
PLE 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd
______________________________________
26* L L L Y Y Y Y Y Y
27* L L Y L L Y Y Y Y
28 N N N N N N N N N
29 N N N N N N N N N
30 N N N N N N N N N
31 N N N N N N N N N
32 N N N N N N N N N
33 N N N N N N N N N
______________________________________
*Controls
EXAMPLE
Sixteen photopolymerizable elements (seven controls) were prepared and
tested as described in Example 1 with the following exceptions: the
photopolymerizable layer for each element had the composition shown in
Table 7 below. Results are shown in Table 8 below.
TABLE 7
__________________________________________________________________________
COMPOSITIONS (PARTS)
SAMPLE
B1
B2
B3
M1 M2 M3 IN1
CT1
LD1
A4
A7
A10
A14
A1
A2
__________________________________________________________________________
34* 21
42 17 6 4 3 3
35 21
42 17 6 4 3 3 4
36 21
42 17 6 4 3 3 4
37* 46 16 17 7 4 3 3
38 46 16 17 7 4 3 3 4
39* 58 29 5 3
40 58 29 5 3 5
41 58 29 5 3 5
42 58 29 5 3 5
43 58 29 5 3 4
44* 58 28 5 3 3
45* 58 29 5 3 3 3
46* 58 29 5 3 3 6
47* 58 29 5 3 3 4
48 58 29 5 3 3 4
49 58 29 5 3 3 4
__________________________________________________________________________
*Controls
TABLE 8
______________________________________
BACKTRANSFER
30 uA, -3.0 kV
50 uA, -7.0 kV
SAMPLE 1st 2nd 3rd 1st 2nd 3rd
______________________________________
34* Y Y Y Y Y Y
35 N N N N N N
36 N N N N N L
37* Y Y Y L Y Y
38 N N N N N N
39* Y Y Y Y Y Y
40 N N N L L L
41 N N N L L L
42 N N N L L L
43 N N N L L L
44* Y Y Y L Y Y
45* L L Y Y Y Y
46* L L Y Y Y Y
47* L L Y Y Y Y
48 N N N N N N
49 N N N N N N
______________________________________
*Controls
EXAMPLE 5
Seven photopolymerizable elements were prepared and tested as described in
Example 1 with the following exceptions: the photopolymerizable layer for
each element had the composition shown in Table 9 below. Results are shown
in Table 10 below illustrating usefulness of mixtures of acidic additives.
TABLE 9
______________________________________
COMPOSITIONS (PARTS)
SAMPLE B1 M1 IN1 CT1 A3 A8 A12 A14 A17
______________________________________
50* 58 28 5 3
51 58 28 5 3 6
52 58 28 5 3 3 1.5
53 58 28 5 3 3 3
54 58 28 5 3 3 1
55 58 28 5 3 4
56 58 58 5 3 3 3
______________________________________
*Control
TABLE 10
______________________________________
BACKTRANSFER
SAM- 30 uA, -3.0 kV
30 uA, -5.0 kV
50 uA, -7.0 kV
PLE 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd
______________________________________
50* Y Y Y Y Y Y Y Y Y
51 N N N N N N L L L
52 N N N N N N L L L
53 N N N N N N L N N
54 N N N N N N N N N
55 N N N L L L L L L
56 N N N N N N L L L
______________________________________
*Control
EXAMPLE 6
This example illustrates the use of the photohardenable electrostatic
master to prepare a four color proof.
The following composition was prepared from the indicated ingredients in
parts:
______________________________________
B2 B3 M2 M3 INI CT1 LDI A4 S2 S1
______________________________________
21.4 44.3 16.4 6.5 3 2 3 3 0.5 0.3
______________________________________
After the solution was stirred for 24 hr to properly dissolve all the
components, it was coated onto aluminized polyethylene terephthalate at
100 ft/min (30.48 m/min) coating speed. Coating weight was 130
mg/dm.sup.2. A polypropylene cover sheet was placed on the photopolymer
surface immediately after drying. The material thus formed was cut into
four pieces about 31 inches by 26 inches (78.7 cm by 66.0 cm) for
preparation of a four color proof.
A four color proof was obtained by following the general procedure for
making a four color proof outlined above using cyan, magenta, yellow and
black photohardenable electrostatic masters.
EXAMPLE 7
Five photopolymerizable elements were prepared as described in Example 1
and tested for adhesion to the substrate using an Instron peel test which
measures the force needed to peel the photopolymerizable layer from the
substrate. Table 11 below shows the composition of each photopolymerizable
element and the peel forces. Larger peel force indicates greater adhesion
to the substrate. Samples 57 and 59 containing the sulfonamides (A4)
showed significantly better adhesion than Samples 58, 60 and 61 which had
p-toluenesulfonic acid (TSA) and triphenylamine (TPA) in the compositions.
TABLE 11
__________________________________________________________________________
COMPOSITIONS (PARTS) AND ADHESION
Peel
SAMPLE
B1 B2 B3 M2 M3 IN1
CT1
LD1
A4
TSA
S2
TPA
S1 Force*
__________________________________________________________________________
57 67.2
17.3
4.6
3 2 2.4
3 0.5 0.03
16.4
58 65.1
16.8
4.2
3 2 2.4 2 0.5
4 0.03
7.3
59 16.6
49.7
18.2
4.6
3 2 2.4
3 0.5 0.03
13.3
60 15.9
47.6
18.1
4.5
3 2 2.4 2 0.5
4 0.03
7.8
61 43.8 15.5
17.2
8.1
4 2 3 3 0.3
3.2
0.03
4.5
__________________________________________________________________________
*Instron peel test, in grams force/linear inch.
An Instron Tensile Tester, Model 1130 with 500 g load cell, and Microcon 1
unit from Instron Corp., Canton, Mass. was used in testing the adhesion of
a photohardenable layer to the conductive substrate. Unexposed film
samples were cut in 1 inch (2.54 cm).times.10.25 inch (26.04 cm) strips.
The cover sheet of the photohardenable element was removed and a piece of
one-inch (2.54 cm) wide transparent Scotch tape (3M Company, Minneapolis,
Minn.) was securely and smoothly attached to the entire coated side of the
film. Approximately one inch (2.54 cm) of the tape plus coating was peeled
from the substrate (aluminized Mylar.RTM. film) and the end of the
uncoated substrate was placed into the top clamp. The free end of the tape
was folded onto itself to form a tab which was then placed into the bottom
clamp. As the crosshead moved upward (at 20 inches (50.8 cm) per minute)
the photohardenable layer was delaminated from the substrate and the peel
force required for the delamination was measured which reflected the
adhesion of the photohardenable layer to the substrate. Five specimens
were tested on each sample. The average peel forces for Sample 57 to 61
are shown in Table 11.
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